JPS6046334A - Preparation of tungsten carbide base sintered hard alloy - Google Patents

Abstract

PURPOSE:To obtain a WC base sintered hard alloy having a fine grain structure, high strength and high toughness, in the title preparation method according to a powder metallurgical method, by using a compound of a Co-W-M (wherein M is a specific metal) system or a system further containing C and N and carbon as a powdery stock material. CONSTITUTION:As a powdery stock material, a powdery mixture consisting of one or more of powdery compound selected from a Co-W-M system, a Co-W- M-C system and a Co-W-M-C-N system (wherein M is one or more of a transition metal belonging to the Groups IVa, Va, VIa of the Periodic Table except W) and a carbon powder are used. This powdery mixture is formed into a green compact which is, in turn, sintered under vacuum or in N2-atmosphere to decompose the aforementioned compound and fine carbides or carbonitrides of WC, Co and M are formed. By this method, a WC base sintered hard alloy having a fine grain structure with an average particle size of about 0.8mum or less in the dispersing phase thereof, high strength and high toughness is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the production of tungsten carbide (hereinafter referred to as WC) cemented carbide having a fine grain structure in which the average grain size of carbides and carbonitrides forming a dispersed phase is approximately 0.8 μm or less. It is about law.

In general, the main component is WC particles that form the dispersed phase, and 4a of the 401 table excludes W as the dispersed phase forming component.
, 5a, and 6a group transition metal carbides and nitrides, and solid solutions of two or more of these (hereinafter collectively referred to as gold-stain, carbon-carbon, and ≧-dide).
The dispersed phase contains 0.1 to 40 inches (by weight, the same applies hereinafter) of one or more species, and the binder phase forming component Co
WCC cemented carbide, which is made of bonded materials, is used in cutting tools, PFI-resistant materials, and impact-resistant tools, and plays an important role in industry. These W.C.C.
Among cemented carbides, those with a fine grain structure in which the average grain size of WC particles is 1 μm or less are suitable for cutting tools with relatively low cutting speeds such as end mills, drills, and paper cutting blades, as well as cold wear-resistant tools. It exhibits excellent performance when used as a powder, but due to recent demands for improved productivity, it has been made into finer particles.
There is a trend toward demand for WCC cemented carbides with high strength and high toughness.

Furthermore, this type of WCC cemented carbide with a fine grain structure is usually processed using a powder metallurgy method using a mixed powder consisting of fine WC powder, Co powder, and metal carbon/nitride powder as the raw material powder. It is manufactured by sintering.

However, the finest commercially available WC powder is 0.5
Some WC powders have an average particle size of about μm, but since this WC powder is easily oxidized, it is not only difficult to handle, but also has questionable quality stability. There is also the problem that cavities are likely to form in the sintered body, resulting in a decrease in strength. In addition, in this type of WCC cemented carbide, the resistance to crank propagation at the interface between the dispersed phase and the binder phase is relatively high, but the resistance to crank propagation at the interface between the dispersed phases is low.
For example, when used as a cutting tool, there is a problem in that the cutting speed is slow, so the rigid material is welded, and when the material is peeled off, fracture occurs at the interface between the dispersed phases, resulting in a decrease in toughness.

Therefore, from the above-mentioned viewpoint, the present inventors conducted research to obtain a WCC cemented carbide having high strength and high toughness by making the dispersed phase, especially WC particles, into fine particles. As long as WC powder is used as the raw material powder, the average particle size of the WC particles in the resulting WCC cemented carbide will be approximately 0.05 mm even if a metal carbon/nitride powder that has a high grain growth suppressing effect is blended. The limit is 8 μm, and it is not possible to make the particles finer than this.
As long as powder is used, it cannot be completely pulverized during mixing due to its ductility, remaining as coarse 00 particles and causing voids in the sintered body, and furthermore, the mixing of WC powder and Co powder Since it is impossible to avoid contact between KWC powders, it is impossible to completely prevent interfacial destruction in the sintered body. Co-W-M-C type compound powder, and Co-W-M-C-N type compound powder (however, M in the above compound is the circumference jυ excluding W).
1 Table 4 a.

One or more of the transition metals of Groups 5a and 6a, C is carbon and N is crab element) is used.9 Then,
Since these compound powders have extremely brittle properties, they can be easily pulverized into fine powders, so there is no residual coarse Co powder as would be the case when a better Co powder is used as the raw material powder in the conventional method. Therefore, the generation of cavities caused by coarse Co particles during sintering is almost eliminated.Furthermore, if carbon powder is mixed with this and the green compact is sintered in a vacuum or nitrogen atmosphere, these The compound easily decomposes to form fine WC and Co, as well as carbides or carbonitrides of ``M'', so the sintering conditions may be adjusted to remove the generated WC and the carbides or carbonitrides of ``M'' above. If grain growth is suppressed, the average grain size will be approximately 0.8
A WCC cemented carbide can be obtained which can have an extremely fine grain structure of micrometers or less, has significantly less adhesion between WC particles, and has significantly fewer cavities, and the resulting WCC cemented carbide has high strength and high toughness. We obtained the knowledge that it is possible.

This invention was made based on the above knowledge, and when manufacturing WCC cemented carbide by powder metallurgy, Co-'vV-M compound powder, Co-'vV-M compound powder,
Co-WM-C based compound powder, and Co-WM-
A mixed powder consisting of one or more of the C-N compound powders and carbon powder is used, and this mixed powder is used as a compact in a weep-like shape in a vacuum or in a nitrogen atmosphere. By sintering and separating the compound during sintering to form fine WC and Co, as well as carbides or carbonitrides of M, the average particle size of the dispersed phase is about 0.
It is characterized by the production of WCC cemented carbide having a fine grain structure of 8 μm or less, high strength and high toughness. In this case, in the WCC cemented carbide, the carbide or carbonitride of M is either dissolved in the bonded Co phase or exists as a solid solution with WC.

Furthermore, if the WCC cemented carbide manufactured by the method of the present invention is subjected to hot isostatic pressure treatment (HI P ) to remove a few remaining cavities, the properties can be further improved. It is something.

Next, the method of the present invention will be specifically explained using examples.

Example 1 Co powder with an average particle size of 1.3 μm and W with an average particle size of 0.8 μm were used for the purpose of producing Co-W-VC compound powder without grinding.
C powder, 0.6 μm W powder, same], 811 mV
C powder is prepared, these powder f, Co powder: 1/1%,
WC powder: 21%, W powder; 64%, VC powder; J-%
After dry mixing, in a hydrogen stream at a temperature of:
Co - by holding at 1000°C for 3 hours
A W-V-C compound powder was produced. This Co-W
-V-C type compound powder'fi: When examined by X-ray diffraction, no diffraction lines of individual constituent components or WC diffraction lines appeared, and C02(W,V)4C type compound was the main part. This showed that a small portion of the residue was composed of an unknown compound, confirming that the reaction was completed. Next, 4 strips of carbon black were added to this co-W-■-C compound and mixed for 48 hours in a 7-heel mill.
After drying, the green compact is press-molded into a powder compact, and the green compact is sintered in vacuum at a temperature of 1310°C for 1.5 hours under conditions of J'4+. provided. This WCC cemented carbide obtained by the method 1 of the present invention, Co content: 13%, flexural crab 420' series r f, H, and its 7n extended structure shows that VC is solid dissolved in the binder phase. However, it was not recognized that
It is composed of fine WC and Co, there is no N type A, and the average grain size of Wc particles nz: 0. ] 5thrn fine grain structure.

On the other hand, as raw material powders, the above Co powder, W
Using C powder and VC powder, the blending ratio is -6w
Conventional method 1 was carried out under the same conditions as in method 1 of the present invention, except that C powder: 86%, Co powder = 13%, and VC powder = 1%. WC obtained by this conventional method 1
C cemented carbide, bending crab 290/'7. Furthermore, the ITn average particle size of the Wc particles is as coarse as 0.9 ttm, and it is A according to ASTM standards.
1-A2 bore was recognized.

Example 2 For the purpose of producing the same Co-W-Ti based compound powder, in addition to the Co powder and W powder used in Example 1, TiH2 powder having an average particle size of 3 μm was prepared, and these powders were , Co powder: 32%, W powder: 62%, and TiH2 powder: 6%, and dry mixed. After this, Co was heated in vacuum at a temperature of 950°C for 4 hours. -W-Ti-based compound powder was produced. The resulting Co-W-T i-based compound powder was subjected to an X-ray line. ), Co7(W,Ti)O-type compounds were the main components, and the remaining "Wazugaka unknown compounds" were confirmed.

Next, 8.5 parts of carbon black was added to this Co-W-Ti compound, mixed in a ball mill using an open method, dried, and then press-molded to form a green compact.
This green compact was heated in a nitrogen atmosphere of 1 torr at a temperature of 1
Method 2 of the present invention was carried out by sintering at 290° C. for 3 hours. According to this invention method 2! The manufactured WC cemented carbide exhibited a CO content of 30% and a bending strength of 360 kg/+na, and its structure was also composed of fine WC (!: Co, Sarani (W, Ti) CN). It was composed of a solid solution, had no bores, and had a fine grain structure exhibiting an average grain size of 0.201+m.

On the other hand, the Co used in Example 1 as the raw material powder
Besides powder and WC powder, average particle size: 1.0 tt m
(7) (W, Ti)CN solid solution powder (WC/T
iC/TjN=5/4/1, weight ratio), these powders were mixed into WC powder: 47cm, Co powder=30cm.
%, (W, Ti)CN Solid solution powder = 23% In conventional method 2, which was carried out under the same conditions as in method 2 of the present invention, H,, W was added to the bent crab 250.
Average particle size of c particles: ], 0/Lm, Gatsu ASTM
It was not possible to obtain a WC-based cemented carbide having a bore of A1-A2 according to the standard.

Example 3 Co3 with an average particle size of 1°5 μm for the purpose of spinning -T a -N b -C-based compound powder
0. Powder, 2.0 μm WO, powder, 1.2 μrn
(Ta,Nb)C solid solution carbide powder (TaC/NbC
=9/1, weight ratio) and carbon black were prepared, and these powders were mixed into the following proportions: Co3O4 powder: 9%, WO3 powder = 71%, (Ta, Nb)C powder: 4%, carbon black]C6. After blending and dry mixing,
A Co-W-Ta-Nb-C compound powder was produced by holding it at 950°C for 4 hours in a hydrogen stream.
XI% of compound powder! When examined by diffraction, the diffraction lines of individual constituent components and the 111r&' of WC did not appear, indicating that CO3 (W, Ta, Nb)oc4 type compounds accounted for the main part, and the remaining small portion was due to unknown compounds. It was confirmed that the reaction was completed. Then, 3 was added to this Co-W-Ta-Nb-C compound.
．． Blend carbon black of 5 parts and process 4 parts in a ball mill.
Method 3 of the present invention is carried out by wet mixing for 8 hours, drying, press-forming into a green compact, and sintering this green compact in vacuum at a temperature of 1300'CVC and maintained for 2 hours. did. WCC cemented carbide obtained by this invention method 3, Co content: 9%, bending crab 3 s o ”/-
2, and its structure consists of fine WC and (W, Ta
, Nb) consisting of C solid solution carbide and Co,
There is no bore, and the average particle size of WC particles: 0.20μ
It had a fine grain structure of m.

On the other hand, the above (Ta) is used as the raw material powder.

Nb) In addition to the C powder, the Co powder and WC used in Example 1
Prepare powders and mix these powders with WC powder = 86 candy, Co
In conventional method 3, which was carried out under the same conditions as in method 3 of the present invention, except that powder: 9 parts and (Ta, Nb)C powder = 3 parts, ,
It was not possible to obtain a WCC cemented carbide having an average grain size of wc powder particles of 1/1 mk and having a bore of A2-A3 according to ASTM standards.

Practical example 4 First, for the purpose of producing a Co-W-V-Cr-C based compound powder, the Co powder, W powder, and WC used in Example 1 were used.
In addition to powder and VC powder, average particle size: 2.21z
Prepare Cr3C2 powder of
C powder 2 0.5%, Cr3 C2 powder: I was blended in the ratio of Co powder under the same conditions as the method 1 of the present invention in Example 1.
-W-V-Cr-C based compound powder was manufactured. When this Co W-V-Cr-C based compound powder was examined by X-ray diffraction, no diffraction lines of individual constituent components or WC diffraction lines appeared, indicating that it was a CC3 (W, V, Cr)gC4 type compound. occupies the main part, and the remaining small part consists of an unknown compound, confirming that the reaction was completed. Next, 3.5% carbon blank was added to this C0-W-V-Cr-C based compound, and the present invention was obtained by mixing, molding, and sintering under the same conditions as the method 3 of the present invention in Example 3. Invention method 4 was implemented. This WCC cemented carbide obtained by the method 4 of the present invention, Co-containing TJ
'j (: : !) Section, shows the anti-fracture crab 400 #//・, and 1:, vc to that organization.

m Cr3C2 was not observed as a solid solution in the bonded phase, but
Consisting of fine WC and Co, with no bore and WC
The particles had a fine grain structure with an average particle diameter of 0°15 ft m.

On the other hand, as raw material powders, the above-mentioned Co powder, WC
powder, VC powder, and Cr, C, powder, and the proportions were WC powder: 89.5%, Co powder = 9%, V
C powder: 0.5%, Cl-3C2 powder: ] 1%
In conventional method 4, which was carried out under the same conditions as in method 4 of the present invention except for
．． Average particle size of WC particles: o, 9ttm*, and AS
It was not possible to obtain a WCC cemented carbide with a bore of A2-A3 according to the TM standard.

As described above, according to the method of the present invention, the average particle size of the WC particles is set to about 0.8 μm or less, WC, Co, and metal carbon/nitride are uniformly and finely dispersed, and most of the bore is The WCC cemented carbide has no fine grain structure M&, and therefore can produce high strength and high toughness WCC cemented carbide.

Applicant: Mitsubishi Metals Corporation Agent Tomi 1) Kazuo (external J name)

Claims (1)

[Claims] When producing a tungsten carbide-based cemented carbide by a powder metallurgy method, Co-W-M compound powder, Co-W-M-C compound powder, and C
o -W -M -C-N compound powder (M in the above compound is one or more transition metals of groups 4a, 5a, and 6a of the periodic table excluding W) -1C
Use a mixed powder consisting of carbon powder and one or more of the following: carbon and nitrogen, respectively. A tungsten carbide group having a fine grain structure, characterized in that it is sintered in an ambient atmosphere, and during this sintering, the compound is decomposed to produce fine tungsten carbide and Co, as well as the carbide or carbonitride of the M. Manufacturing method of cemented carbide.